Low-Speed Incident

A client reached out because they had an incident involving a mail truck that impacted a Infiniti SUV. It was a low speed incident where the male truck was delivering mail and ended up backing into the front of a parked SUV. And the driver of the SUV was claiming some injuries to his spine and closed head injuries. And so I was asked to evaluate the incident and determine what was the severity of the collision, and then also what were the forces acting on the occupant? How did those forces relate to the potential injuries that were being claimed? The first thing I want to look at is all the evidence that I have. I was given testimony from both the driver of the SUV and then the driver of the mail truck. The driver of the SUV, he says he actually had his vehicle in park and that he was actually texting on the cell phone at the time, so he was looking down.

Some photos that were taken at the scene. So it actually showed the mail truck and the SUV in the location of where the impact actually occurred. Medical records for the driver of the SUV was given a repair estimate so I could understand what the damage was to the SUV and an incident report.

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For this case, I did inspections of the mail truck in the subject SUV, and then I also inspected the scene. So at the mail truck, I captured the full geometry using a FARO laser scanner, which allows me to capture the geometry of the entire mail truck. I didn't find any damage that was related to an impact. There was just no damage to the rear end of that mail truck. And then I also was able to gather information related to how much the mail truck weighed, which is important in the analysis. And then lastly, I was able to actually do some testing. I drove the mail truck and I used a GoPro mounted to the hood of the mail truck. When we use the GoPro that has a GPS on it, we can get that telemetry data. So we get the speed and acceleration data over a series of different tests.

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For the SUV, I also gathered the exterior geometry using the FARO laser scanner. And then I also got the interior geometry. The driver of the SUV actually drove the SUV to the inspection, so his seat position was documented. The mailbox, the roadway terrain, and then also the geometry of the surrounding areas.

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I did some calculations and then I also did some simulations and was able to get the Delta-V or the change in speed, which is how we quantify the severity of an impact. And so I was able to determine what that Delta-V was experienced by the SUV. And in this particular case, it came out to be a range of one to three miles per hour. In order to determine the forces on the occupant, that's where I then do what's called a biomechanical analysis. So once I understand the Delta-V on the vehicle, I can then calculate how does that correspond to the forces on the occupant. And so for this case, what I did was I took my vehicle simulation, which resulted in a Delta-V of one to three, and then I input it into an occupant simulation. We use a software called Matimo, and that is, again, a physics-based simulation software program.

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And I put him in the vehicle in a position consistent with how he testified, so looking down at a cell phone, and I was able to actually input a delta-v of one and a delta-v of three, and then calculate what were the forces that the occupant actually experienced as a result of a one to three mile an hour Delta-V.

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We know from biomechanics that injuries are caused by a certain application of force. One of the claimed injuries was a disc herniation. So in order to cause a disc herniation, you have to squeeze the spine from top to bottom at the same time that the spine is flexed forward, so bending forward and squeeze from top to bottom. And we know that from the literature where they've actually created disc herniations in the lab on cadavers, that that amount of squeezing from top to bottom, which we call compression, that that compressive force is pretty big. It's a very large number on the order of 1,200 pounds. And I know here's what the compressive force in this incident is, and it's very low on the order of couple hundred pounds. And then I can compare, well, what is a compressive force in the spine when this driver would bend over or maybe when this driver would plop down into a chair and I can compare the compressive force during those events to the compressive force in this event.

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The compression in this event is actually less than what would be experienced when plopping down into a chair.

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